Non-contact cool-down station for wafers

ABSTRACT

A stationary cooling station for cooling wafers after the wafers have been subjected to semiconductor processing supports the wafer by flowing gas in accordance with the Bernoulli principle. An upper wall of the cooling station contains a plurality of gas outlets that direct gas to flow over the top surface of the wafer. In this way, a low-pressure region is created over the wafer and the wafer is suspended within the cooling station, without directly contacting any surface for support. In addition to providing lift for the wafer, the gas is a thermally conductive gas that can cool the wafer by conducting heat away from it.

REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.10/701,681, filed Nov. 4, 2003.

FIELD OF THE INVENTION

This invention relates generally to semiconductor fabrication and, moreparticularly, to an apparatus and a method for cooling a substrate at acool-down station.

BACKGROUND OF THE INVENTION

Semiconductor wafers or other such substrates are subjected to very highprocessing temperatures. For example, in high temperature epitaxialchemical vapor deposition (CVD), the temperatures can approach 1200° C.,while low temperature epitaxy is conducted between about 400° C. and900° C. In a typical cycle, using one or more robotic wafer handlers, awafer is transferred from a room temperature cassette either directly,or via one or more loadlock and transfer chambers, into a processing orreaction chamber where the wafer is subjected to high temperatureprocessing. The wafer is then transferred using one or more waferhandlers from the high temperature processing chamber back to the samecassette or a separate cassette for processed wafers, either directlyfrom the processing chamber or via the loadlock and transfer chambers.

Because of the high temperature CVD processing, transport of the waferfrom the process chamber immediately to, e.g., a wafer cassette is notpossible due to the temperature of the wafer exceeding the limits ofheat resistance of the materials commonly used in the cassettes. Atthese temperatures, the cassettes may be damaged and the structuralintegrity of the cassette may be undermined. Because of this, transferof the wafer to the cassette must be postponed until the wafertemperature falls below the limits of the thermal materials propertiesof the cassette material. While cassettes are available that can handlewafers as hot as 170° C., they are relatively expensive. A commonlyavailable and less expensive cassette made of Delrin® can only handletemperatures well below 100° C. Other commonly available units can onlyaccomodate wafer temperatures of about 60° C.

Similarly, transfer of the wafers to a loadlock chamber immediatelyafter high temperature processing is not possible because thetemperature of a just-processed wafer may exceed the limits of the heatresistance of materials typically used to support the wafers in aloadlock. As such, the structural integrity of the wafer support devicesin the loadlock chamber may be undermined and the loadlock may bedamaged. Consequently, it is necessary to cool the temperature of thewafer to levels suitable for contact with the surfaces of a cassette ora loadlock.

Because wafer handling and processing typically occur in an enclosed andcarefully controlled environment, there are three principle locations orpoints during the cycle where the cooling of the wafer might occur: thewafer could be cooled on the susceptor on which it is supported in theprocess chamber, on the wafer handling device, or off-line at somelocation within the apparatus between the process chamber and thecassette or loadlock. Cooling the wafer on the susceptor is notcost-effective, however, because the process chamber is then unavailablefor processing another wafer, thereby reducing the system waferthroughput. This approach is particularly unattractive because it isthen necessary to incur the delay and cost of reheating the wafersupport structure or the chamber generally (in the case of hot wallchambers). Removing a wafer while it is hot and cooling it on the waferhandling device is better, but also not cost effective because the delayin loading the next wafer slated for processing also compromisesthroughput, or requires additional wafer handling equipment and room foraccommodating the same. Such impediments increase the per-wafer cost,making these approaches financially unattractive to end users. Becauseof the high cost of semiconductor wafer processing equipment, it is, ofcourse, critically important from a competitive standpoint to be able tokeep this expensive processing equipment in continued use so as toincrease the throughput. At the same time, the wafer cooling techniqueemployed must be compatible with the environment of the CVD processingapparatus so as not to adversely affect stringent cleanlinessrequirements. Also, the cost of the technique must itself besufficiently moderate so that there is a net reduction in per-wafercosts.

Use of off-line cooling chambers for cooling a wafer can be moreefficient, since the susceptor and wafer handling device are notoccupied by the wafer being cooled. In conventional cooling chambers, awafer is positioned on pins in the chamber and cooled by conduction orconvection, e.g., by flowing cooling gases over the surfaces of thewafer. Because of the high temperature of the wafer, these pins aretypically constructed of quartz or silicon carbide. This approach tocooling wafers also has drawbacks, however, as the relatively hard pinscan damage and leave scratches on the backside, or bottom surface, ofthe wafers by the force of the wafers being placed upon the pins. Inaddition, contraction of a wafer while it cools on the pins can furtherscratch the wafer.

Accordingly, it is an object of this invention to provide an improvedsystem for quickly cooling wafer-like substrates to a temperature thatwill allow the use of low cost commonly available cassettes, while notcausing damage to the bottom surface of the wafer.

SUMMARY OF THE INVENTION

In accordance with one preferred embodiment of the invention, a systemis provided for high temperature semiconductor processing. The systemcomprises a semiconductor substrate, a high temperature processingchamber and a substrate handling chamber having a port for moving thesubstrate into or out of the processing chamber and also a port formoving the substrate to and from a storage area into or out of thehandling chamber. The system also includes an automatic substratehandler in the handling chamber for transporting the substrate to andfrom the storage area and into and out of the process chamber. Alsoincluded in the system is a cooling station into which the substratehandler can move the substrate to cool the substrate after processingand before returning the substrate to the storage area. The substrate issupported in the cooling station without a bottom surface or a topsurface of the substrate contacting a cooling station surface at anytime. The cooling station is configured to support the substrate byemitting a gas in accordance with the Bernoulli principle.

In accordance with another preferred embodiment, a semiconductor waferholding station is provided for holding semiconductor wafers. The waferholding station comprises a ceiling and a floor defining a wafer spacetherebetween for accommodating a wafer. The wafer holding station alsocomprises a stationary gas outlet assembly operating in accordance withBemoulli's principle. The gas outlet assembly has a plate that comprisesa first axis extending forwardly and rearwardly along a horizontalsurface of the plate. A first plurality of outlets is provided in theplate on one side of the first axis for exhausting gas received by theassembly into the wafer space and for establishing a plurality ofstreams of gas flow toward a perimeter of the wafer upon retention ofthe wafer. A second plurality of outlets is also provided in the plateon another side of the first axis for exhausting the gas received by theassembly into the wafer space and for establishing a plurality ofstreams of gas flow toward the perimeter of the wafer upon retention ofthe wafer. A central outlet disposed generally coincident with the firstaxis is also provided in the plate for exhausting the gas received bythe gas outlet assembly and for establishing a flow of gas intermediatethe plurality of streams of gas flow emanating from the first and secondplurality of outlets upon retention of the wafer. The gas outlets areconfigured to exhaust the gas at an angle and direction to create a lowpressure zone adjacent the wafer.

In accordance with yet another preferred embodiment of the invention, asemiconductor wafer cooling station is provided. The cooling stationcomprises an upper horizontal surface and a lower horizontal surface.The upper horizontal surface and the lower horizontal surface define awafer space configured to accommodate a semiconductor wafer. The coolingstation also comprises an immobile cooling assembly having a pluralityof gas outlets configured to exhaust a gas onto a face of the wafer. Thecooling assembly is configured to suspend the wafer by the Bernoulliprinciple utilizing the plurality of gas outlets, with all faces of thewafer vertically separated from the upper and the lower horizontalsurfaces.

In accordance with another preferred embodiment of the invention, amethod is provided for cooling a hot substrate that has been subjectedto high temperatures in a chamber. The method comprises removing the hotsubstrate from the chamber with a substrate handler and transferring thehot substrate into a stationary cooling station using the substratehandler. The substrate is vertically suspended inside the coolingstation in accordance with the Bernoulli principle by flowing a gas tocreate a low pressure zone across a horizontal surface of the substrate.The handler is withdrawn from the cooling station and the substrate isconvectively cooled by flowing the gas across the substrate's horizontalsurface.

In accordance with another preferred embodiment of the invention, amethod is provided for semiconductor processing. The method comprisessubjecting a substrate to high temperature processing in a processchamber and providing a substrate handler capable of transportingsubstrates into and out of the process chamber. The substrate iswithdrawn from the process chamber using the substrate handler aftersubjecting the substrate to high temperature processing. Subsequently,the hot substrate is transported by the handler into a cooling stationand aligned with a plurality of gas outlets in the cooling station. Thehandler is removed from the cooling station and the substrate issupported in the cooling station only by flowing a gas out of the gasoutlets and across the substrate. The method further comprises removingthe substrate from the cooling station.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood from the detailed description ofthe preferred embodiments and from the appended drawings, which aremeant to illustrate and not to limit the invention, and wherein:

FIG. 1 is a perspective, schematic view of a wafer handling chamber andadjacent portions of a CVD apparatus, in accordance with preferredembodiments of the invention;

FIG. 2 is a cross-sectional view of the wafer handling chamber and waferinput or output chambers of FIG. 1;

FIGS. 3A, 3B and 3C are schematic, cross-sectional views of a waferstation, in accordance with preferred embodiments of the invention;

FIGS. 4 is a plan view, in isolated, of a horizontal surface of thewafer station of FIGS. 3A and 3B, in accordance with preferredembodiments of the invention; and

FIGS. 5 is a side cross-sectional, schematic view of a semiconductorprocessing system with one form of a wafer handler that can be used withthe wafer station, in accordance with preferred embodiments of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the illustrated embodiments, a wafer station is provided in which asemiconductor wafer or substrate is held suspended by gas flowing acrossa major surface of the substrate in accordance with Bernoulli'sprinciple. By this flow of gas, the substrate can be suspended without ahorizontal surface of the substrate contacting another surface forvertical support. Advantageously, the wafer station can be used as acooling station to cool substrates after undergoing semiconductorprocessing. In such an arrangement, the gas flowing across the majorsurface can be a cooling gas that cools the substrate as it flows acrossthe major surface. In other arrangements, the wafer station can be usedas a staging area to temporarily hold a wafer before the wafer istransported elsewhere.

In suspending the substrate by taking advantage of the Bernoulliprinciple, the wafer station operates in a manner similar to a class ofsemiconductor pick-up devices called Bernoulli wands. Bernoulli wandsare shown in U.S. Pat. Nos. 5,080,549 and 6,183,183 B1, both to Goodwin,et al., the disclosures of which are herein incorporated by reference intheir entirety. In particular, jets of gas are flowed from gas outletsin the wafer station at angles toward the substrate to create a regionof low pressure above the substrate, therefore lifting it inarrangements in which the gas outlets are located above the substrate.The weight of the substrate and the pressure of gas exiting the gasoutlets provide countervailing forces that advantageously prevent thesubstrate from being draw into contact with the gas outlets. Anadvantage of such a wafer station is that the substrate need not contactsurfaces of the wafer station, except perhaps at one or more smalllocations at the side of the substrate, where the substrate can touchpins that help to center the substrate under the gas outlets. In otherarrangements, the gas outlets can also be located beneath the substrate,as the gas flowing out of the gas outlets can generate sufficientpressure to suspend the substrate over the gas outlets while maintaininga low pressure zone under the wafer to prevent the wafer from skatingoff the station. The gas can be any gas compatible for use insemiconductor processing systems, although, preferably, in arrangementsfor cooling the substrate, the gas is a highly thermally conductiveinert gas.

Reference will now be made to the Figures, wherein like numerals referto like parts throughout.

FIGS. 1 and 2 illustrate a portion of a chemical vapor deposition (CVD)apparatus in which wafer station 20 can be housed, in some preferredembodiments of the invention. The CVD apparatus includes a schematicallyillustrated automatic or robotic wafer handler 22 centrally positionedwithin a handling chamber 24. The chamber upper wall 24 a isschematically shown in FIG. 2, but is not shown in FIG. 1 so as toillustrate internal components in the chamber 24. The handling chamber24 is connected to load/unload chambers 26 by way of one or moreload/unload ports 28. FIG. 1 illustrates an arrangement in which onechamber 26 functions as a load chamber and another chamber 26 functionsas an unload chamber. Either may be referred to as a storage area. FIG.2 shows a single one of those chambers 26. Many systems utilize a singlechamber 26 from which a wafer is withdrawn for processing and is thenreturned after processing. The handling chamber 24 is further connectedto a processing chamber 30, schematically illustrated in FIG. 1, by wayof a processing port 32 through a sidewall 24 b of the handling chamber24. Gates or valves are normally provided for the load/unload port 28and the processing port 32, but these are not shown for purposes ofsimplicity.

In accordance with preferred embodiments of the invention, there isprovided at least one wafer station 20 in one portion of the waferhandling chamber 24 adjacent the process chamber 30. The wafer station20 is preferably positioned out of the path of the handler so as not tointerfere with movement and rotation of the handler 22. Thus, asubstrate can be moved out of the process chamber 30 and cooled whileanother substrate is moved from one of the chambers 26 into the processchamber 30 for processing. In the illustrated embodiment, a second waferstation 20 is also provided on the other side of the processing port 32adjacent the wall 24 b leading to the process chamber 30. In thisarrangement, the wafer handler can move a substrate from one of thechambers 26 to the process chamber 30 while one or both of the waferstations 20 are occupied with a substrate. Advantageously, thesearrangements can increase throughput by minimizing periods when theprocess chamber 30 is not actively processing a substrate.

With reference to FIG. 2, each wafer station 20 has a wafer space 34which is sized to receive one wafer in a horizontal position, and thewafer station is preferably open to the area of the handling chamber 24in which the wafer handler 22 is positioned so that wafers may be movedinto and out of the wafer station 20 by the handler 22. Preferably, aspart of the cooling station control system, a sensor (not shown) is usedto detect the presence or absence of wafers 38 in the cooling station20. In addition to being able to temporarily hold a wafer (i.e., as astaging area), each wafer station 20 preferably also functions as awafer cooling station for cooling wafers after the wafers have, e.g.,undergone semiconductor processing. Each cooling station 20 includes agas outlet assembly 36, as seen in FIG. 2. It should be noted that whilethe gas outlet assembly 36 is illustrated located above the wafer 38, inother embodiments the assembly 36 can be located below the wafer 38.

With reference to FIGS. 3A, 3B, 3C and 4, the gas outlet assembly 36preferably includes a plate 41 and a base 40 having a gas inlet 42 thatis connected to a suitable source of gas (not shown). Preferably, asillustrated, the gas inlet 42 is centrally located with respect to thebase 40 to provide for a uniform flow of gas to the gas outlets 44.While illustrated as having a disc-shaped base 40 and plate 41 standingout from the ceiling of the cooling station 24, it will be appreciatedthat the gas outlet assembly 36 need not have a disc-shaped base 40 orplate 41. Rather, the gas outlet assembly 36 can be part of any surfaceof the cooling station 24 facing the central region of the station andcan have any shape, so long as the surface comprises gas outlets 44oriented to allow gas to flow across the wafer 38 for enabling theBernoulli principle to be used to suspend the wafer 38 in the coolingstation 20, as discussed in greater detail below with respect to FIG. 4.

With reference to FIG. 3A, it can be seen that the cooling station 20can include a single gas outlet assembly 36 to both cool and todischarge gas to lift the substrate 38 by the Bernoulli principle. Inother embodiments, cooling of the substrate 38 is augmented by othermeans. For example, as illustrated in FIG. 3B, a showerhead assembly 46can be positioned in the cooling station 20 directly opposite the gasoutlet assembly 36. The gas outlet assembly 36 is located adjacent theupper wall 24 a of the handling chamber 22 and the showerhead assembly46 is supported on the shelf, or wafer station floor, 24 d. Togetherwith the upper wall 24 a, the gas outlet assembly 36 constitutes aceiling for the wafer station 20. In addition, just as the gas outletassembly 36 has a gas inlet 42, the showerhead assembly 46 has a gasinlet 48 that is connected to a suitable source of gas (not shown).Advantageously, by this arrangement, substrate cooling can beaccelerated by directing cooling gas to both major horizontal surfacesof the substrate 38, i.e., by gas flows 58 and 60 to the top surface 38a and gas flow 47 to the bottom surface 38 b.

In other arrangements, as shown in FIG. 3C, the gas outlet assembly 36can be located beneath the substrate 38. Flowing gas out of the gasoutlet assembly 36 in accordance with the Bernoulli principleadvantageously provides a cushion of gas to vertically suspend thesubstrate 38 while, as discussed below, also providing a force tomaintain the substrate 38 centered over the gas outlet assembly 36. Theflow rate of the gas is chosen sufficient to produce the cushion of gas;advantageously, the flow rate in this arrangement typically need not bealtered relative to the gas flow rate used when a gas outlet assembly 36is located directly above a substrate 38. While not shown, a showerheadcan also be provided above the substrate 38.

It will be appreciated that the gas outlet assembly 36 is provided withgas outlets that emit gas to a substrate at angles, to suspend thesubstrate in the wafer station 20. The gas flow angle and flow rate arechosen such that, flowing across a major surface of the substrate, thegas flow causes an area of decreased pressure for enabling the BernoulliPrinciple to be used to hold the substrate suspended in the coolingstation 20 without physical contact with support structures.Advantageously, the gas can be any gas compatible for use insemiconductor processing systems, preferably including but not limitedto inert gases such as nitrogen, argon, helium, neon, etc. Morepreferably, for cooling the substrate, the gas flowing over thesubstrate is a highly thermally conductive inert gas, such as helium orargon.

One exemplary arrangement of gas outlets is shown in FIG. 4. FIG. 4 is aplan view of the gas outlet assembly 36, with the gas outlets 44 and 62and gas channels 54 and 56 for transporting gas to the gas outlets 44and 62 schematically illustrated. It will be appreciated that thesurface 52 is oriented so that it faces the substrate 38, when thesubstrate 38 has been loaded into the cooling station 20. Under thesurface 52, the gas channel 54 is formed between the base 40 (FIGS.3A-3C) and the plate 41, and is preferably formed by a channel machinedinto one or the other or both of the base 40 and the plate 41. The gaschannel 54 extends along a first axis along the surface 52, andcommunicates with a gas source (not shown) through the gas inlet 42. Theextension of the first axis in one arbitrary direction can be consideredan extension forwardly along the axis and the extension in the oppositedirection can be considered an extension rearwardly along the axis.

A plurality of transverse gas passages 56 intersects the gas channel 54to provide gas flow to various parts of the area on either side of thegas channel 54. A number of gas outlets 44 extend from both the gaschannel 54 and the transverse gas passages 56 to the surface 52 of thegas outlet assembly 36 facing the wafer space 34. The gas outlets 44provide the Bernoulli flow for suspending substrates, as discussedabove.

The flow of lifting gas proceeds from the gas inlet 42 to the gaschannel 54 and continues into the transverse gas passages 56. The gas ispreferably distributed at a uniform pressure throughout the channel 54and passages 56 and exits from the gas outlet assembly to provide auniform and efficient lifting velocity. Specifically, some of the gasoutlets 44 are angled to provide gas flow such as indicated at 58, whileother of the gas outlets are angled as indicated by the flow arrow 60 toprovide flow in a generally opposite direction. As illustrated, the flowof gas is preferably radially outward from the approximate center of gasoutlets 44 so as to provide a continuous outwardly sweeping air flow forkeeping particles off the top surface of the wafer while simultaneouslyproviding the area of decreased pressure for enabling the BernoulliPrinciple to be used to lift or pick up the wafer without physicalcontact. In addition, a central gas outlet 62 is preferably providedextending perpendicularly to the surface of the plate 41. The centralgas outlet jet 62 advantageously provides an additional gas flow tosweep out particulates which might otherwise flow into the reducedpressure region directly adjacent the plate 41. Suitable sweep jets arediscussed in U.S. Pat. No. 5,080,549 to Goodwin, et al., the disclosureof which is herein incorporated by reference in its entirety.

Preferably, the number of gas outlets 44 angled as indicated by 58outnumber the number angled as indicated by 60, to induce a slight forceon the levitated wafer 38 (FIGS. 3A-3C) in the direction of the stopelement 64. In other embodiments, larger gas outlets 44 angled asindicated by 58 can be provided to accomplish the same result. Byslightly directing the substrate 38 to contact the stop elements 64,which prevents the substrate 38 from further drifting in the directionof the flow 58, the substrate 38 can be kept centered under the gasoutlets 44. The wafer stop elements 64 are curved to conform to theshape of the wafer in the cooling station 20, and have a plurality ofstop pegs 66 which can directly contact sides of the substrate.Preferably, there are three such stop pegs 66 distributed along the arcof each stop element 64.

In addition, the stop elements 64 are preferably positioned opposite theopening of the cooling station 20 through which the substrate 38 entersthe cooling station 20. In this arrangement, the stop elements 64 do notinterfere with the movement of the substrate 38 into and out of thecooling station 38. It will be appreciated, however, that the stopelements 64 can be positioned at other locations, so long as there is nointerference with the movement of the substrate 38 into and out of thecooling station 20. In addition, to prevent being damaged by a hotsubstrate 38, the stop elements 64 are preferably formed of quartz, orother high temperature resistant material, including non-scratchingmaterials such as Teflon®.

Further details regarding one exemplary embodiment of the wafer station20 are described below. As illustrated in FIG. 4, at least three gasoutlets 44 are located on either side of the gas channel 54. In theillustrated embodiment, seven gas outlets 44 and one central gas outlet62 are located in the plate 41 of the gas outlet assembly 36. The gasoutlets 44 and central gas outlet 62 each have a diameter of about 0.019inch±about 0.001 inch. In addition, in contrast to the more generallyvertical gas jets of standard showerheads, the gas outlet holes 44 areoriented at an angle of about 30°±about 1° relative to a plane formed bythe gas outlet holes 44, e.g., relative to the surface 52 of the gasoutlet assembly 36 in the illustrated embodiment. The central gas outlethole 62 is oriented perpendicular to the surface 52. The flow rate ofgas through each gas outlet 44 is about 7 to 10 slm, with a totalaggregate flow of gas out of all gas outlets 44 being about 60 to 70slm. Four gas outlets 44 are located laterally of the axis 54 and areoriented to discharge gas in the direction 58. An additional gas outlet44 is located coincident with and rearwardly along the axis 54 and alsodischarges gas as indicated by 58. Two gas outlets 44 are locatedlaterally of and forwardly along the axis 54 and are oriented todischarge gas in the opposite direction, as indicated by 60. It will beappreciated that the rate of cooling of the substrate can be altered byincreasing or decreasing the rates of flow of gas across the substrate'ssurface. It will also be appreciated that the cooling rate can befurther increased by use of a showerhead to flow cooling gas to thesubstrate from the side of the substrate opposite the gas outletassembly 36. As discussed earlier, the cooling gas can including, e.g.,nitrogen, argon, helium and hydrogen. Moreover, the exact number andsize of the gas outlets can vary, depending, for example, upon the sizeof the wafer.

With reference to FIG. 5, the substrate 38 is preferably transportedinto the cooling station 20 after processing in the processing chamber30. After being cooled to a temperature low enough for the substrate 38to be received in commonly available relatively low-cost wafercassettes, preferably about 60° C. or less, the substrate 38 istransported out of the cooling station 38 to the load/unload chambers26, which can contain wafer cassettes 68 for storing the substrates 38.The pick-up arm 70 preferably picks up the wafer 38 off the rotatablesusceptor 72 in the processing chamber 30, on which the wafer 38 canundergo semiconductor processing, and transports the wafer 38 to thecooling station 20. While illustrated with the wafer handling chamber 24directly adjacent to the processing chamber 30 and the load/unloadchambers 26, it will be appreciated that the substrate can travelthrough various other chambers, such as load lock chambers, thatintervene between the processing chamber 30 and the load/unload chambers26 in other arrangements. In yet other arrangements, the wafer station20 can be a stand-alone station located adjacent to the illustrated CVDapparatus. The skilled artisan will appreciate that, while described asa cassette for ease of discussion and illustration, reference numeral 68can be any structure, e.g., a cassette, a FOUP or a boat, for storingwafers.

The wafer handler 22 and pick-up arm 70 for transporting the substrate38 to and from the cooling station 20 can be any of the varioussubstrate handling systems known in the art, some non-limiting examplesof which are discussed below. As discussed earlier, one type ofsubstrate pick-up device, known as a Bernoulli wand, flows gas downwardfrom the wand toward the wafer that then radially outward to create aregion of lower pressure between the wafer and the wand, thereby liftingit. The Bernoulli wand advantageously avoids contact with the wafer,except, perhaps, at one or more small edge locators. One type ofBernoulli wand is shown in U.S. Pat. No. 5,080,549 to Goodwin, et al.Advantageously, in an embodiment where the cooling station gas outletsare located underneath a wafer 38 (FIG. 3C), the use of a Bernoulli wandto handle the wafer 38 allows the wafer 38 to be transported and cooledor staged without being directly contacted, other than with theaforementioned edge locators or stop elements 64 (FIG. 4). In additionto transporting the substrate 38 to and from the cooling station 20, aBernoulli wand can advantageously elevate, transport the wafer 38 out ofthe process chamber 30 and start cooling at the station 20 of FIG. 3Cwhile it is still at very high temperatures.

Another type of wafer pick-up wand utilizes a vacuum force and, thus,must be in intimate contact with the wafer. U.S. Pat. No. 4,566,726 toCorentti, et al. discusses a combination of Bernoulli and vacuum pick-updevices.

Yet another type of wafer pick-up device is a simple paddle or,preferably, a fork, both of which lifts and supports wafers fromunderneath. Many suitable paddles or forks are known in the art, withparticular non-limiting examples of paddles or forks described below.

One exemplary paddle is illustrated in U.S. Pat. No. 4,951,601 toMaydan, et al. That patent also illustrates a typical movement devicefor translating wafers from location to location within processingsystems. The wafer handler is capable of linear retraction andextension, as well as rotation about an axis. U.S. Pat. No. 5,135,349 toLorenz, et al., discloses a robotic handling system using twopaddle-type pick-ups mounted on a common rotating base. Both pick-upsare adapted to extend linearly away from one another to speed handlingof wafers within the processing system. The paddles are augmented with avacuum generated through a plurality of holes in an end effector portionof each paddle; the vacuum being transmitted along a channel within thepaddle. Consequently, it will be appreciated that any of these or otherwafer handling systems known in the art can be modified or adapted foruse with the cooling station 20.

To transport a wafer 38 into or out of the processing chamber 30, thewafer handler 22 can be rotated to be aligned with the process chamber30. Generally, after processing, the wafer is too hot to transferdirectly to the load/unload chamber 26. Instead, the wafer handler isrotated a small distance to align with one of the cooling stations. Thepick-up arm 70 is then extended to place the hot wafer 38 into thecooling station 20. The flow of gas out of the gas outlets 44 (FIG. 4)then generates a low pressure region proximate the face of the wafer 39facing the gas outlet assembly 36 to draw the wafer 38 towards the gasoutlet assembly 36 without directly contacting the gas outlet assembly36. The pick-up arm 70 can then be retracted. Inside the cooling station20, the wafer 38 can be cooled by the flow of gas across one or more ofits surfaces.

While the first wafer is being cooled, a second wafer can be positionedinto the process chamber. This second wafer may be retrieved from thecassette 68 and transferred to the processing chamber 30, or the secondwafer may have been positioned into the second cooling station while thefirst wafer was being processed. In that case, the handler only has tobe rotated a short distance (about 100°) from the first cooling station20 to align the wand with the second cooling station to withdraw asecond wafer, and then rotate back (about 50°) to the position where thesecond wafer can be inserted into the process chamber 30. The secondcooling station in that situation is serving as a staging area. Afterthe second wafer has been placed into the process chamber 30, the firstwafer 38 can be removed from the first cooling station 20 and returnedto the storage area 26, assuming it has been adequately cooled by then.Immediately after placing a processed wafer 38 into the storage area, athird wafer can be withdrawn from the cassette 68 and moved to one ofthe cooling/staging stations to await its turn to be placed in theprocess chamber 30. From the foregoing, it can be appreciated that greatflexibility is provided in the handling of the wafers so that the waferscan be moved in various sequences to fit with the temperatures and timesof the processes being used by the system and with the time required tocool the particular wafers to the temperature desired before returningthe wafer to the standard cassette 68.

Based on the foregoing, it will be appreciated that the wafer stationadvantageously allows a wafer to be cooled without having to rest onpins or other support structures. As such, the wafer station desirablyprevents scratching of the wafer's bottom surface, as can happen whenthe bottom surface rests directly on a support structure.

It will also be appreciated that although this invention has beendescribed on the basis of particular preferred embodiments,modifications of the invention are possible and are within the spiritand scope of this disclosure. For example, while a single processchamber has been illustrated and discussed, a so-called cluster systemcould be employed wherein additional process chambers may be clusteredaround the wafer handler. With the arrangement shown at least twoadditional chambers could be provided. Consequently, these and variousother omissions, additions and modifications may be made to theprocesses described above without departing from the scope of theinvention, and all such modifications and changes are intended to fallwithin the scope of the invention, as defined by the appended claims.

1. A semiconductor substrate-holding station for holding a semiconductorsubstrate, comprising: a ceiling and a floor defining a substrate spacetherebetween for accommodating a substrate; a stationary gas outletassembly configured to operate in accordance with Bernoulli's principle,the gas outlet assembly having a plate, the plate comprising: a firstaxis extending forwardly and rearwardly along a horizontal surface ofthe plate; a first plurality of outlets on one side of the first axisfor exhausting gas received by the assembly into the substrate space andfor establishing a plurality of streams of gas flow toward a perimeterof the substrate upon retention of the substrate; a second plurality ofoutlets on another side of the first axis for exhausting the gasreceived by the assembly into the substrate space and for establishing aplurality of streams of gas flow toward the perimeter of the substrateupon retention of the substrate; and a central outlet disposed generallycoincident with the first axis for exhausting the gas received by theassembly and for establishing a flow of gas intermediate the pluralityof streams of gas flow emanating from the first and second plurality ofoutlets upon retention of the substrate, wherein outlets are configuredto exhaust the gas at an angle and direction to create a low pressurezone adjacent the substrate.
 2. The semiconductor substrate-holdingstation of claim 1, wherein the horizontal surface faces downwards. 3.The semiconductor substrate-holding station of claim 2, furthercomprising a showerhead for exhausting gas upwards into the substratespace, the showerhead located opposite the plate.
 4. The semiconductorsubstrate-holding station of claim 1, wherein the first plurality ofoutlets numbers at least three.
 5. The semiconductor substrate-holdingstation of claim 4, wherein the second plurality of outlets numbers atleast three.
 6. The semiconductor substrate-holding station of claim 5,further comprising a rear central outlet in the plate, the rear centraloutlet disposed generally coincident with the first axis and rearwardlyof the central outlet.
 7. The semiconductor substrate-holding station ofclaim 1, wherein a diameter of each of the outlets is between about0.018 and about 0.020 inch.
 8. The semiconductor substrate-holdingstation of claim 1, wherein an angle of orientation, with respect to thehorizontal surface, of each outlet of the first and the second pluralityof outlets through the plate is substantially similar.
 9. Thesemiconductor substrate-holding station of claim 8, wherein the outletsare angled between about 29° and about 31° with respect to thehorizontal surface.
 10. The semiconductor substrate-holding station ofclaim 9, wherein a majority of the outlets point rearwardly.
 11. Thesemiconductor substrate-holding station of claim 10, further comprisingone or more substrate obstructions positioned rearwardly of the plate,the obstructions configured to contact an edge of the substrate and tomaintain the substrate positioned under the gas outlet assembly, uponretention of the substrate.
 12. A semiconductor substrate holdingstation, comprising: an upper horizontal surface and a lower horizontalsurface defining a wafer space configured to accommodate a semiconductorwafer; and an immobile gas discharge assembly, the gas dischargeassembly having a plurality of gas outlets configured to exhaust a gasonto a face of the wafer, wherein the gas discharge assembly isconfigured to suspend the wafer by the Bernoulli principle utilizing theplurality of gas outlets, with both faces of the wafer verticallyseparated from the upper and the lower horizontal surfaces.
 13. Theholding station of claim 12, wherein the gas outlets are in gascommunication with an inert gas source.
 14. The holding station of claim13, wherein the inert gas source contains nitrogen gas.
 15. The holdingstation of claim 13, wherein the inert gas source contains a highlythermally conductive gas.
 16. The holding station of claim 15, whereinthe thermally conductive gas comprises helium.
 17. The holding stationof claim 15, wherein the thermally conductive gas comprises argon. 18.The holding station of claim 12, wherein the cooling assembly providesgas flow through the upper horizontal surface to the wafer space. 19.The holding station of claim 18, further comprising a showerhead toprovide gas flow through the lower horizontal surface to the waferspace.
 20. The holding station of claim 19, wherein the cooling assemblyprovides gas flow through the lower horizontal surface to the waferspace.